What is the reason behind malicious?

[norwyn]

Gossip? And slandering someones name?

[valentino]

When one person despite being really pretty, or great in all senses is not convinced of own greatness beauty and all such qualities feels the need to talk about another person in a derisive manner, they are being slanderous.

This is a very human quality. If one person does not recognize his or her own worth then all their time is spend on rumor mongering, gossiping and slandering another person. The reason for this is insecurity. Such a person obsesses about another for no reason but that of hatred and always tries to one up on the others.